The invention relates to a motor brake arrangement for an internal combustion engine with a compressor with an air intake duct leading to the engine and an exhaust duct connected to an exhaust gas turbine, and a cutoff valve disposed in the exhaust duct upstream of the compressor.
DE 28 24 598 C2 discloses a motor brake arrangement for an internal combustion engine with an exhaust gas turbocharger which includes a shut-off valve disposed in an exhaust gas duct between the engine and the turbine of a turbocharger. The cutoff valve is a rotary valve with a pivotable valve body whose axis extends normal to the exhaust gas duct. The cutoff valve has a normal open position wherein the exhaust gases are admitted to the turbine of the turbocharger in an uninhibited manner. In the closed position of the shut-off valve, a residual exhaust gas flow is still admitted to the turbine of the turbocharger whereby the turbine wheel of the turbine is kept at a minimum speed.
US Pat. No. 3,591,959 discloses a motor brake arrangement for an internal combustion engine with a shut-off valve by which a front and rear exhaust manifold of a six-cylinder engine can be blocked.
Both motor brake arrangements with exhaust gas shut-off valves arranged upstream of the turbocharger have the disadvantage that turbine power is reduced essentially to zero when the shut-off valve is closed. As a result, the turbocharger speed is also reduced so that the engine is not being charged during such periods. The braking energy that can be transferred to the air mass flow is therefore greatly limited by the reduced air flow. Accordingly, a high required braking power results in high temperature of the air discharged from the engine such that the temperature stresses of the engine are relatively high. During braking operation, there is, furthermore, a need for a high exhaust gas manifold pressure with such arrangements if a high braking power is needed whereby the problem of valve floating may occur. The exhaust gas pressure in the exhaust gas manifold may exceed the closing force of the exhaust valves whereby the motor braking effectiveness is further reduced.
It is the object of the invention to provide a motor brake arrangement for an internal combustion engine with an exhaust gas turbocharger wherein the motor braking performance is increased with a relatively low temperature load of the motor and the exhaust system.